The purpose of this study was to investigate class differences in the responses of infants to tape recordings of mothers' and strangers' voices. Subjects were 10-month-old first-born Caucasian girls, 30 from middle class families and 30 from working class families. Stimuli presented through a speaker placed in front of the infant consisted of taped passages read by the subject's own mother, and by a stranger from her own social class group. Codings were made of each subject's vocalizations, smiling, looking at speaker baffle, looking at mother, and looking at coder. Two additional measures taken were heartrate deceleration and physical activity. Middle class infants responded differentially to the two stimuli, while working class infants did not. The most dramatic differences involved the infants' looking behaviors. Middle class infants looked more at their mothers after hearing their mother's voice, and more at the coder following the stranger's voice, which may be related to the fact that these infants have experienced more verbal stimulation from their mothers at home. The present findings are consistent with previous investigations of infant reaction to language stimuli. [Not available in hard copy due to marginal legibility of original document.] (NH)